Antigenic differences between the cystozoite and endozoite of Toxoplasma gondii have been found. Using fluorescent antibody antisera against the cystozoite reacted positive against only the cystozoite. Antisera against the endozoite reacted positive against both endozoite and cystozoite. Absorption of sera with endozoites removed only positive reactions with endozoites. These findings are the first to suggest antigenic differences between the zoites within the cyst and zoites outside the cyst of toxoplasma.